This invention relates to a method and apparatus for introducing into a container a material to be dispensed in aerosol form and a propellant therefor. The invention is particularly concerned with the introduction of pharmaceutical materials into containers, and the following description concentrates on this. It is to be understood, however, that the invention can also be applied to other materials.
Conventionally, pharmaceutical materials which are to be dispensed in aerosol form are usually suspended in a mixture of at least two propellants, at least one of which has a high enough boiling point to be liquid at room temperature, and at least one of which has a low enough boiling point to be a gas at room temperature.
For convenience, these are referred to below as a liquid, or low pressure, propellant, and a gaseous, or high pressure, propellant respectively. The pharmaceutical material is first suspended in the liquid propellant by a mixing operation. Each aerosol container is then partly filled with this suspension. A quantity of the gaseous propellant is then introduced into each of the containers using either a cold-fill method or a high-pressure method. In the former, the filling operation is carried out at a temperature sufficiently below room temperature for the gaseous propellant to be liquid. Each container is then closed by a closure which includes an outlet valve through which the contents of the container can subsequently be dispensed. In the high-pressure method, the closure is applied to the container before the gaseous propellant is introduced, and that propellant is introduced subsequently into each container by forcing it under pressure into the container through the outlet valve, which during this operation acts in effect as an inlet valve.
No satisfactory method currently exists for filling a container with a suspension or solution of a pharmaceutical in a single or multi-component propellant which is gaseous at room temperature. It is an object of one aspect of the present invention to provide such a method, and to provide an apparatus for carrying out that method.
FIG. 1 shows the introduction into a container C of a suspension of a pharmaceutical material in a liquid propellant. Vessel 1 contains a bulk supply of this suspension which is pumped by a pump 2, through a non-return valve 3, into a metering cylinder 4 provided with a vent 5. From there, the suspension passes to a filling head 8. In the inoperative condition the suspension passes through the head 8 to a non-return valve 9 and thence back to the vessel. The suspension is thus kept constantly in circulation. When a quantity of suspension is to be introduced into the container C, the container is positioned below the head 8, and the valves 3 and 9 are closed. The pneumatic cylinder 6 is then operated to force the piston therein downwardly, thus increasing the pressure in the suspension trapped between the valves 3 and 9 to a level sufficiently to open a valve in filling head 8 and to cause suspension to pass from the filling head into the container C. The valves 3 and 9 are then opened and the valve in filling head 8 shut, and when the piston in the cylinder 6 is withdrawn to its original position the cylinder 4 refills from the vessel 1. Movement of the filling nozzle into and out of engagement with each can is effected by a piston and cylinder arrangement 7. The filling head 8 is arranged to operate only when it is in engagement with a container C.
The apparatus of FIG. 1 introduces into container C a suspension of pharmaceutical material in a liquid propellant, and after an aerosol valve is crimped on the can C the apparatus shown in FIG. 2 operates on it to introduce gaseous propellant. The apparatus of FIG. 2 is formed of components which are substantially the same in principle as corresponding components of FIG. 1, except that there is nothing corresponding to the non-return valve 9 and there is no recycling. Components in FIG. 2 are denoted by reference numerals which correspond to those used in FIG. 1, with the addition of 10. The vessel 11 contains gaseous propellant only, under sufficient pressure for it to be a liquid, and contains no pharmaceutical material.
When the apparatus of FIG. 2 is in operation, a small quantity of gaseous propellant escapes each time the filling head 18 is lifted from a container C. This is of no particular consequence provided the amount of propellant lost in this way is small.
However, this feature of the operation of the apparatus of FIG. 2 means that were it used for introducing into a container a suspension or solution of a pharmaceutical material in a high pressure propellant, it would be entirely unsatisfactory. It can be seen that if vessel 11 contained such a suspension or solution, what would escape each time the filling head 18 was lifted from a container would be a quantity of such a suspension or solution. This would present a hazard to workers involved in the operation, and where the pharmaceutical material concerned was an expensive one, could also represent a significant financial loss. Furthermore, the escaped pharmaceutical material would tend to deposit on the surrounding part of the apparatus and on the exterior of the container itself, giving rise to problems of cleaning. The first of these problems could be avoided, in theory, by surrounding the apparatus of FIG. 2 by an exhaust system, though this would involve considerable expense. The other two problems would not be avoided even by such an exhaust system.